Method and apparatus for transceiving signals in a distributed antenna system

ABSTRACT

The present invention relates to a terminal which receives signals from a base station, and to a method in which the terminal receives signals from the base station in a distributed antenna system (DAS). The terminal receives, from the base station having a plurality of antennas, control information on one or more active transmission antennas allocated to the terminal, from among the plurality of antennas, and receives signals from the base station via said one or more active transmission antennas.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for transceiving signals ina distributed antenna system.

BACKGROUND ART

Recently, the ongoing development of information industry demands atechnology of transmitting large-scale data of various types at highspeed. To this end, many ongoing efforts are made to research anddevelop DAS for the solution to the shadow region problem and thecoverage extension by means of a plurality of distributed antennasprovided within a conventional cell.

Distributed antenna system (hereinafter abbreviate DAS) is the systemthat utilizes a plurality of distributed antennas connected with asingle base station via wired or dedicated circuit. In this case, thesingle base station manages a plurality of antennas situated within acell managed by the base station in a manner of being spaced apart fromeach other over a predetermined distance. Considering the fact that aplurality of the antennas are distributed and situated within the cellin a manner of being spaced from each other over the predeterminedspace, the distributed antenna system is discriminated from acentralized antenna system (hereinafter abbreviated CAS). The CASincludes such a cellular communication system as WCDMA (wideband codedivision multiple access), HSPA (high speed packet data), LTE/LTE-A(long term evolution/long term evolution-advanced) and 802.16. And, theCAS is the system that uses such a multi-antenna scheme as OL-MIMO (openloop-multi input multi output), CL-SU-MIMO (close loop-single user-multiinput multi output), CL-MU-MIMO (close loop-multi user-multi input multioutput), Multi-BS-MIMO (multi-base station-multi input multi output) andthe like in a manner of installing multiple antennas on a single basestation in a cell based structure.

The DAS may differ from a femto cell in that a base station at a cellcenter controls and manages all distributed antenna areas situatedwithin a cell instead of enabling each unit of distributed antennas tocontrol and manage an area of the corresponding antenna. Considering thefact that the distributed antenna units are connected via the wired ordedicated circuit, the DAS may differ from a multi-hop relay system oran ad-hoc network in which a base station and a remote station (RS) areconnected by wireless. Moreover, considering the fact that thedistributed antennas are able to transmit different signals to userequipments adjacent to the corresponding antennas, respectively, the DASis discriminated from a repeater that amplifies and transmits a signalonly.

Considering that distributed antennas are able to support a singlemobile station or multiple mobile stations by transceiving differentdata stream at the same time, the DAS may be considered as a sort of amultiple input multiple output (MIMO) system. In aspect of MIMO system,the DAS may provide an effect of reducing transmission power owing tothe antennas distributed to various locations within a cell in a mannerthat a transmission area of each antenna is reduced smaller than that ofthe CAS. Moreover, the DAS enables fast data transmission by decreasinga path loss through a reduction of a transmission distance between anantenna and a user equipment, thereby raising transmission capacity andpower efficiency of a cellular system. And, the DAS may satisfy acommunication performance quality relatively more uniform that that ofthe CAS irrespective of a user's location within a cell. Moreover, sincea base station is connected with a plurality of distributed antennas viathe wired or dedicated circuit, the DAS has small signal loss andlowered inter-antenna correlation and interference to provide a highsignal to interference plus noise ratio (SINR).

Thus, the DAS reduces the costs for base station expansion and backhaulnetwork maintenance in a next generation mobile communication system andextends a service coverage, and enhances channel capacity and SINR,thereby becoming a new base of a cellular communications together withthe conventional CAS or by being substituted for the CAS.

DISCLOSURE OF THE INVENTION Technical Problem

Accordingly, the present invention is directed to substantially obviateone or more problems due to limitations and disadvantages of the relatedart. First of all, an object of the present invention is to provide amethod of performing a communication, in which a base station transmitssystem related control information to user equipments entering a DAScell to support DAS.

Another object of the present invention is to provide a method ofperforming a communication in a manner of transmitting information on adistributed antenna independently assigned per user equipment or anantenna group due to DAS properties, information on a pilot pattern perantenna and the like.

Another object of the present invention is to provide a method for auser equipment having entered a DAS cell to create and transmit feedbackinformation including antenna related information in order for a DASbase station to efficiently allocate antenna resource per userequipment.

A further object of the present invention is to provide a method ofperforming channel estimation by converting a pilot pattern indextransmitted by a DAS base station to be used for each user equipment toa consecutively enumerated logical antenna index, by which a userequipment can perform channel estimation efficiently.

Technical tasks obtainable from the present invention are non-limitedthe above-mentioned technical task. And, other unmentioned technicaltasks can be clearly understood from the following description by thosehaving ordinary skill in the technical field to which the presentinvention pertains.

Technical Solution

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a method ofreceiving a signal, which is received from a base station by a userequipment in a distributed antenna system (DAS), according to oneembodiment of the present invention may include a step 1) of receivingcontrol information on at least one effective transmitting antennaallocated to the user equipment among a plurality of antennas from thebase station including the plurality of antennas and a step 2) ofreceiving the signal via the at least one effective transmitting antennafrom the base station.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, a user equipment in a distributedantenna system (DAS) according to one embodiment of the presentinvention may include a receiving module configured to receive a signal,a processor configured to generate a feedback information on adistributed antenna of a base station used for a downlink transmissionbased on a downlink signal received from the base station including aplurality of antennas spaced apart from a predetermined distance via thereceiving module and a transmitting module configured to transmit thefeedback information to the base station, wherein the processor isconfigured to receive control information on at least one effectivetransmitting antenna to be used for a communication with the userequipment among the plurality of antennas from the base station via thereceiving module.

According to each embodiment of the present invention, the controlinformation may include at least one selected from the group consistingof information on the number of the at least one effective transmittingantenna, index information of the at least one effective transmittingantenna and received signal strength information for each of theplurality of antennas.

According to each embodiment of the present invention, the method mayfurther include the step of mapping at least one PAI to logical antennaindexes (LAI) according to a predetermined mapping rule. And, thepredetermined mapping rule may configure the LAI with an index of theeffective transmitting antenna in performance order according to a powergain for each effective transmitting antenna.

According to each embodiment of the present invention, the controlinformation may include at least one selected from the group consistingof information on one or more pilot pattern indexes (PPI) supportive ofthe user equipment and information on PPI having an interferenceinfluence on the user equipment.

According to each embodiment of the present invention, the method mayfurther include the step of transmitting feedback information includingantenna related information used for a transmission of a downlink signalbased on the downlink signal received from the base station by the userequipment to the base station before the step 1). In this case, thecontrol information may be determined by the base station based on thefeedback information.

According to each embodiment of the present invention, the feedbackinformation may include at least one selected from the group consistingof a received signal strength for each of the plurality of antennas, asignal received signal strength for at least one antenna selected fromthe plurality of antennas by the user equipment, information on thenumber and/or indexes of antennas meeting a predetermined selectionreference, and candidate PPI meeting a predetermined selectionreference.

And, the predetermined selection reference comprises whether a receivedsignal strength of the downlink signal received via a portion of theplurality of antennas is equal to or greater than a reference value.

According to each embodiment of the present invention, the feedbackinformation may include preferred pilot pattern indexes (PPPI) requestedby the user equipment and the PPPI may include at least one PPI in whicha received signal strength or a channel gain of a channel estimated viaa common pilot transmitted from the base station meets a value equal toor greater than a predetermined reference value.

According to each embodiment of the present invention, the feedbackinformation may further include at least one selected from the groupconsisting of channel state information estimated from each PPI includedin the PPPI, a preferred order of at least one PPI included in the PPPI,a specific number of most preferred PPIs among the at least one PPIincluded in the PPPI, and channel state information on the specificnumber of the most preferred PPIs.

According to each embodiment of the present invention, the specificnumber of the most preferred PPI may correspond to one selected from thegroup consisting of system configuration parameter information,indication information determined and transmitted by the base station,and information arbitrarily determined by the user equipment.

According to each embodiment of the present invention, the controlinformation may include at least one selected from the group consistingof information on specific pilot pattern indexes (PPI) supportive of theuser equipment, an index set (excluded PPI: e-PPI) supposed to beexcluded from the candidate PPI or the PPPI fed back from the userequipment, and an index agreement indicator indicating whether PPI equalto the candidate PPI or the PPPI fed back from the user equipment isused.

According to each embodiment of the present invention, if the indexagreement indicator is set to indicate the information indicating thatthe PPI equal to the candidate PPI or the PPPI fed back from the userequipment is used, the control information may not include informationon the specific PPI and the e-PPI.

According to each embodiment of the present invention, the method mayfurther include the step of mapping the specific PPI to LAI by apredetermined mapping rule. And, the predetermined mapping rule mayinclude configuring the LAI in performance order according to power gainfor each of the PPI.

In this case, the method may further include the steps of estimatingchannel related information based on the LAI and transmitting thechannel related information to the base station by feedback.Alternatively, the method may further include the step of transmittinginformation on the predetermined mapping rule to the base station.

According to each embodiment of the present invention, the controlinformation may be independently configured for each user equipmentbelonging to the DAS and the control information may be determinedindependently in accordance with at least one of a location of the userequipment and a frequency band used by the user equipment.

According to each embodiment of the present invention, the method mayfurther include the step of receiving indication information indicatingthat the system supports at least one of the DAS and a centralizedantenna system from the base station when the user equipment enters acell area in which the base station provides a service. In this case,the indication information may be transmitted via cell ID.

According to the above-described embodiments of the present invention,an antenna or an antenna group may be used together with an antenna portin LTE/LTE-A.

The above embodiments are just parts of preferred embodiments of thepresent invention. And, it is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory and are intended to provide further explanation of theinvention as claimed.

Advantageous Effects

According to the above-described embodiments of the present invention, acommunication can be performed in a manner that a DAS base stationtransmits system related control information to user equipments enteringa DAS cell.

According to the above-described embodiments of the present invention, aDAS base station can perform a communication in a manner of transmittinginformation on a distributed antenna or an antenna group independentlyassigned for each user equipment due to DAS properties, information on apilot pattern for each antenna and the like.

According to the above-described embodiments of the present invention, auser equipment can generate and transmit feedback information includingantenna related information in order for a DAS base station toefficiently allocate antenna resource for each user equipment.

According to the above-described embodiments of the present invention, auser equipment can efficiently perform a channel estimation byconverting a pilot pattern index transmitted by a DAS base station to beused for each user equipment to a consecutively enumerated logicalantenna index.

Effects obtainable from the present invention may be non-limited by theabove mentioned effect. And, other unmentioned effects, objects andfeatures of the present invention can be clearly understood from thefollowing description by those having ordinary skill in the technicalfield to which the present invention pertains.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram for one example of a DAS structure for theapplication of the present invention.

FIG. 2 is a diagram for another example of a DAS structure for theapplication of the present invention.

FIG. 3 is a diagram for one example of a process for transceivingsignals between a base station and a user equipment in DAS according toone embodiment of the present invention.

FIG. 4 is a diagram for another example of a process for transceivingsignals between a base station and a user equipment in DAS according toone embodiment of the present invention.

FIG. 5 is a diagram for another example of a process for transceivingsignals between a base station and a user equipment in DAS according toone embodiment of the present invention.

FIG. 6 is a diagram for another example of a process for transceivingsignals between a base station and a user equipment in DAS according toone embodiment of the present invention.

FIG. 7 is a diagram for one example of a process for a DAS base stationto transmit signals to a user equipment according to one embodiment ofthe present invention.

FIG. 8 is a diagram for another example of a process for a DAS basestation to transmit signals to a user equipment according to oneembodiment of the present invention.

FIG. 9 is a block diagram of a base station and a user equipment toimplement embodiments of the present invention.

BEST MODE FOR INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. In the following detailed description of the inventionincludes details to help the full understanding of the presentinvention. Yet, it is apparent to those skilled in the art that thepresent invention can be implemented without these details. Forinstance, although the following descriptions are made exemplarily usingIEEE 802.16 system for clarity, the following descriptions areapplicable to various wireless communication systems including 3GPP(3^(rd) generation partnership project) system and the like.

Occasionally, to prevent the present invention from getting vaguer,structures and/or devices known to the public are skipped or can berepresented as block diagrams centering on the core functions of thestructures and/or devices. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Besides, in the following description, assume that a terminal is acommon name of such a mobile or fixed user stage device as a userequipment (UE), a mobile station (MS) and the like. And, assume that abase station is a common name of such a random node of a network stageconfigured to communicate with a terminal as a Node B, an eNode B, a BS,a processing server (PS) and the like.

FIG. 1 is a diagram for one example of a DAS structure for theapplication of the present invention.

First of all, a base station shown in FIG. 1 may include a plurality ofantennas situated at a cell center in accordance with CAS. For clarityof the following description, DAS antennas are shown in FIG. 1 only. InDAS, a plurality of antennas connected by wire with a single basestation located in a cell are distributed at various locations withinthe cell. And, the DAS can be implemented in various ways in accordancewith the number and locations of the antennas. For instance, a pluralityof antennas may be distributed within a cell be being spaced evenlyapart from each other or at least two antennas may be intensivelylocated at a specific place. In the DAS, no matter what kind offormation is made in a cell by the distributed antennas, when thecoverage of the antennas are overlapped, a signal transmission over arank 2 becomes possible. In this case, a rank indicates the number ofdata streams simultaneously transmittable via at least one antenna.

Referring to FIG. 1, a single base station providing a service for asingle cell area is connected by wire with total 8 antennas. And, therespective antennas may be situated in a cell in a manner of beingspaced apart from each other over a predetermined distance by apredetermined interval or various intervals. In DAS, it may beunnecessary to use all antennas connected with a base station. And, anappropriate number of antennas may be useable based on a signaltransmission range of each antenna, a coverage overlapping extent withan adjacent antenna, an effect of interference with an adjacent antenna,a distance between an antenna and a mobile station (or user equipment)and the like.

For instance, referring to FIG. 1, when 3 user equipments UE 1 to UE 3are located within a cell and the UE 1 is situated within signaltransmission ranges of antennas 1, 2, 7 and 8, the UE 1 may be able toreceive signals from at least one of the antennas 1, 2, 7 and 8. On theother hand, in aspect of the UE 1, since each of antennas 3, 4, 5 and 6has a considerable interval between an antenna and a user equipment, itmay be highly possible to generate a path loss and increase powerconsumption. And, a signal transmitted from each of the antennas 3, 4, 5and 6 may have a negligible value.

For another instance, since the UE 2 is located in a part where thesignal transmission range of the antenna 6 overlaps with that of theantenna 7, a signal transmitted via another antenna except the antenna 6and the antenna 7 is negligibly small or weak. Since the UE 3 is locatedwithin an adjacent distance of the antenna 3, it may be able toexclusively receive signals transmitted via the antenna 3.

In the DAS, as shown in FIG. 1, if locations of a plurality of antennasare spaced far apart from each other within a cell, the DAS may workline MIMO system. The base station communicates with the UE 1 via anantenna group 1 consisting of at least one of the antennas 1, 2, 7 and8, communications with the UE 2 via an antenna group 2 consisting of atleast one of the antenna 6 and the antenna 7, and communicates with theUE 3 via the antenna 3, at the same time. In doing so, the antenna 4 andthe antenna 5 performs transmission for the UE 3 and the UE 2,respectively, or may operate by being turned off.

In particular, in the DAS (distributed antenna system), the number ofdata streams transmitted per user equipment in case of the communicationwith a single user or multiple users may be diversified and antenna orantenna group allocated to each user equipment located within a cellserviced by a base station may exist in various ways. In accordance witha location or located place of the mobile station situated within thecell, it may be able to specify the antenna or the antenna group, whichperforms communication with the corresponding user equipment. Yet, theantenna or the antenna group may be adaptively changeable in accordancewith the movement of the mobile station within the cell.

FIG. 2 is a diagram for another example of a DAS structure for theapplication of the present invention. In particular, FIG. 2 shows oneexample of a system structure when DAS is applied to a centralizedantenna system that uses the cell based multiple antennas of the relatedart.

Referring to FIG. 2, in a cell area for a base station to provide aservice, since an antenna interval at a central part of the cell areaadjacent to the base station is very small in comparison with a cellradius, a plurality of centralized antennas (CAs) having such a similareffect as a path loss and the like may be located. Moreover, in anoverall area of the cell, since an antenna interval is wider than thatof CA, a plurality of distributed antennas (DAs) having such a differenteffect per antenna as a path loss and the like may be located in amanner of being spaced apart over a predetermined distance from eachother.

The DA consists of at least one antenna connected with a base station bywire and may be used for the same meaning of a DAS antenna node or anantenna node. In particular, the antenna node includes at least oneantenna and the at least one antenna configuring each antenna node isconnected by wire as well. At least one or more DAs form a DA group toconstruct a DA zone.

The DA group includes at least one DA. The DA group may be configuredvariably in accordance with a location of a user equipment, a receptionstate or the like or may be configured fixedly with the maximum numberof antennas used in MIMO. According to IEEE 802.16m, the maximum antennanumber amounts to 8 Tx. The DA zone is defined as a range for antennasconfiguring the DA group to transmit or receive signals. The cell areashown in FIG. 2 includes n DA zones. A user equipment belonging to theDA zone may be able to perform communication with at least one DAconfiguring the DA zone. And, a base station may be able to raise atransmission rate using both DA and CA simultaneously in case oftransmitting a signal to the user equipment belonging to the DA zone.

FIG. 2 shows CAS including DAS to enable a base station and a userequipment to use the DAS in CAS structure using multiple antennas of therelated art. Locations of CA and DAs are illustrated in a manner ofbeing discriminated from each other for clarity, by which the locationsare non-limited. And, the CA and DAs may be located in various ways inaccordance with an implementation type.

Thus, in DAS, the number of data streams per user equipment may existvariously in case of SU/MU MIMO communication, a specific antenna or aspecific antenna group may be allocated to each user equipment, and aspecific antenna or a specific antenna group allocated to acorresponding user equipment may be changed by real time.

Therefore, when a user equipment enters a cell area in which a serviceis provided by a DAS supportive system, the present invention intends topropose a DAS operating method for a base station of DAS system todetermine a specific antenna or a specific antenna group supportive of acommunication with the corresponding user equipment and the DASoperating method for transceiving signals between a base station and auser equipment belonging to the DAS via signaling of the determination.

In this specification, a transmitting antenna of DAS may become the atleast one distributed antenna or the antenna group mentioned in theforegoing description or may be interchangeably used together with theDA or the DA group mentioned in the foregoing description.

In case that LTE/LTE-A system supports DAS, the antenna or the antennagroup described with reference to FIG. 1 or FIG. 2 may beinterchangeably used together with at least one antenna port. In thefollowing description of the embodiments of the present invention, anantenna or pilot pattern may be substituted with an antenna port.

1. 1^(st) Embodiment Antenna Resource Allocation Via Uplink SignalMeasurement

In a DAS operating method according to one embodiment of the presentinvention, a DAS base station may be able to determine a specificantenna or a specific antenna group used for a downlink signaltransmission to a user equipment based on an uplink signal transmittedfrom the user equipment.

FIG. 3 is a diagram for one example of a process for transceivingsignals between a base station and a user equipment in DAS according toone embodiment of the present invention.

Referring to FIG. 3, a base station belonging to a DAS according to oneembodiment of the present invention receives an uplink (UL) signal suchas data, pilot, feedback information, ACK/NACK(acknowledgement/no-acknowledgement) signal and the like from a userequipment having entered a cell area in which the base station providesa service [S301].

The base station then may determine a transmitting antenna for thecorresponding user equipment among all antennas based on a result ofmeasuring a strength of the received UL signal. According to thistransmitting antenna determination, it may be able to allocate anantenna resource in consideration of various conditions including a loadstate of the base station, intra-cell distribution of user equipments,cooperation with an adjacent cell and the like. For instance, by theantenna resource allocation, at least one transmitting antenna may befinally determined for each of user equipments or each group of userequipments among all antennas of the base station [S302].

Subsequently, the base station may transmit DAS control informationincluding information on the transmitting antenna corresponding per userequipment or user equipment group via a control channel, and preferably,via a dedicated control channel [S303].

Table 1 shows one example of DAS control information according to oneembodiment of the present invention.

TABLE 1 DAS control information i Number of transmitting antennas for aspecific user equipment or a specific user equipment group ii Indexinformation of a transmitting antenna a base station intends to use fora specific user equipment or a specific user equipment group iiiInformation on received signal strength per transmitting antenna

Referring to Table 1, DAS control information according to oneembodiment of the present invention may include at least one of i)number of transmitting antennas which a base station intends to use fora corresponding user equipment, ii) index information of a transmittingantenna which a base station intends to use for a corresponding userequipment, and iii) a received signal strength for each transmittingantenna.

In this case, since transmitting antenna information on a correspondinguser equipment may be changed in accordance with a location of the userequipment, distance from a base station antennas and the like, the DAScontrol information may be independently variable for each userequipment. Hence, the base station may be able to transmit the DAScontrol information by predetermined periods. Alternatively, the basestation may be able to transmit the DAS control information only ifnecessary for an event occurrence in the user equipment or the basestation or the like.

Subsequently, the base station may be able to transmit a signal on atransmitting antenna (or an antenna group) specified according to theantenna allocation information on the corresponding user equipmentincluded in the DAS control information [S304].

Besides, the user equipment may perform channel estimation for each ofone or more transmitting antennas specified to the corresponding userequipment based on the received signal and may be then able to transmitthe corresponding feedback information to the base station (not shown inFIG. 3).

FIG. 4 is a diagram for another example of a process for transceivingsignals between a base station and a user equipment in DAS according toone embodiment of the present invention.

A DAS base station according to one embodiment of the present inventionmay be able to transmit antenna resource allocation information forallocating a specific antenna for each of user equipments among allantennas via pilot pattern information on the corresponding antenna.

In this specification, a pilot may include such a signal as a midambleconfigured independently for each antenna, a cell-common referencesignal (CRS), a channel state information-reference signal (CSI-RS) andthe like. Different pilot pattern may be independently used for eachantenna or the same pilot pattern may be used for at least two antennas.For instance, in case that a plurality of antennas use the same pilotpattern, a user equipment receiving signals via the plurality ofantennas may be able to recognize the received signals as a signaltransmitted via a single antenna. Hence, in case that a pilot patternindex (PPI) is used as antenna resource allocation information, it maybe represented as the number of independent pilot patterns allocated toantennas effectively specified to a corresponding user equipment insteadof the number of physical antennas. For instance, if the number oftransmitting antennas specified to a predetermined user equipment is 5and the same pilot pattern is allocated to 3 of the 5 antennas, the PPIfor the corresponding user equipment may be 3.

Referring to FIG. 4, a step S401 for a base station to receive such a ULsignal as data, pilot, feedback information, ACK/NACK signal for datareception confirmation and the like from a user equipment [S401] and astep S402 of determining a transmitting antenna for the correspondinguser equipment among all antennas of the base station based on a resultof measuring a strength of the received UL signal may correspond to theformer step S301 and the former step S302 shown in FIG. 3, respectively.In doing so, the base station may be able to determine a pilot patternused by the antennas for the corresponding user equipment or thecorresponding user equipment group instead of the antenna number and/orindex information during allocating antenna resource per user equipmentor user equipment group. In particular, for another example of antennaresource allocation, it may be able to determine PPI for each of userequipments or each of user equipment groups. For clarity of thefollowing description, the same description shall be omitted.

Subsequently, the base station may transmit DAS control informationincluding information on the transmitting antenna for the correspondinguser equipment [S403].

Table 2 shows another example of DAS control information according toone embodiment of the present invention.

TABLE 2 DAS control information i Pilot pattern indexes (PPI) for a userequipment or a user equipment group ii (Optional) Interference PPIsupporting another user equipment in the vicinity of a correspondinguser equipment

Referring to Table 2, DAS control information according to oneembodiment of the present invention may include pilot pattern indexes(PPI) as transmitting antenna allocation information for a userequipment.

And, the DAS control information may further include information on PPI(hereinafter named ‘interference PPI’) supportive of another userequipment in the vicinity of a corresponding user equipment optionally.For instance, the interference PPI may be defined as PPI that causesinterference to a target user equipment because it supports a differentuser equipment despite affecting the target user equipment. Theinterference PPI may be transmitted at a time different from a time(e.g., period) of transmitting PPI or may not be transmitted. After auser equipment has received DAS control information including PPI, theuser equipment may scan signals transmitted via pilot pattern other thanPPI. If the user equipment is able to determine dominant signals asinterference PPI among the scanned signals, separate interference PPImay not be included in the DAS control information.

Having received the DAS control information from the base station, theuser equipment may be able to derive the information on the transmittingantenna supportive of the corresponding user equipment from the basestation antennas via the PPI. Moreover, the user equipment generatesfeedback information by measuring channel related information includingchannel quality information (CQI), precoding matrix index (PMI),covariance matrix and the like [S404]. The user equipment may be thenable to transmit the generated feedback information to the base station[S405].

In this case, if the interference PPI is included in the received DAScontrol information, the user equipment may derive the information onthe interfering antennas for the corresponding user equipment using theinterference PPI and may be then able to determine such feedbackinformation as PMI for reducing interference and the like.

A method of configuring PMI for antennas to minimize interference foreach of distributed antennas or each of antenna groups may becategorized into a best companion scheme and a worst companion scheme.If the best companion scheme is used, a user equipment determines PMIfor minimizing interference effect from adjacent interfering antennasand may be then able to feed back the determined PMI to a base station.If the worst companion scheme is used, a user equipment determines PMIfor maximizing interference effect from adjacent interfering antennasand may be then able to feed back the determined PMI to a base station.In particular, this feedback information may include such information asbest/worst companion PMI of the interfering antennas for thecorresponding user equipment.

The base station configures a precoding matrix for the transmittingantenna allocated to the corresponding user equipment in considerationof the PMI included in the feedback information to enhance receptionperformance and may be then able to transmit a downlink (DL) signal[S406].

Moreover, in case that the base station receives the PMI for theinterfering antennas from a specific user equipment by feedback, thebase station configures a precoding matrix to minimize interference on aspecific user equipment in case of transmitting a signal to a differentuser equipment using the interfering antennas and may be then able totransmit a signal. Moreover, the base station may be able to change anantenna for the corresponding user equipment or an antenna group for thedifferent user equipment.

2. 2^(nd) Embodiment Antenna Resource Allocation Via Downlink SignalMeasurement

In a DAS operating method according to another embodiment of the presentinvention, a base station belonging to DAS may be able to determine atransmitting antenna or an antenna group for a user equipment based onfeedback information on an antenna resource transmitted from thecorresponding user equipment.

FIG. 5 is a diagram for another example of a process for transceivingsignals between a base station and a user equipment in DAS according toone embodiment of the present invention.

Referring to FIG. 5, a user equipment enters a cell area in which a DASbase station according to one embodiment of the present inventionprovides a service or is moving in a DAS area. In doing so, the userequipment receives a DL signal transmitted from the base station via atleast one distributed antenna [S501]. The user equipment measures thereceived signal and may be then able to generate feedback information.For example, the feedback information may include related information ona transmitting antenna [S502].

Table 3 shows one example of feedback information generated by a userequipment belonging to DAS according to one embodiment of the presentinvention.

TABLE 3 Feedback information i Received signal strength for eachtransmitting antenna used in DL ii Received signal strength of atransmitting antenna used for feedback by a user equipment among alltransmitting antennas used in DL iii Number of transmitting antennasrequested again by a user equipment iv Number of transmitting antennasmeeting an antenna resource selection reference v Index information of atransmitting antenna requested again by a user equipment among alltransmitting antennas in DL vi Index information of a transmittingantenna meeting an antenna resource selection reference among alltransmitting antennas in DL

Referring to Table 3, the feedback information determined by a userequipment may include at least one of i) a received signal strength foreach transmitting antenna used in DL, ii) a received signal strength ofa transmitting antenna used for feedback by a user equipment among alltransmitting antennas used in DL, iii) the number of transmittingantennas requested again by a user equipment, iv) the number oftransmitting antennas meeting an antenna resource selection reference,v) index information of a transmitting antenna requested again by a userequipment among all transmitting antennas in DL, and vi) indexinformation of a transmitting antenna meeting an antenna resourceselection reference among all transmitting antennas in DL. Feedbackinformation may be configured as a bitmap. In case that the transmittingantenna index information in v) and the transmitting antenna indexinformation in vi) are transmitted via a bitmap, each bit configuringthe bitmap may be configured to indicate a transmitting antenna index.

In this case, one example of the antenna resource selection referencemay include a received signal strength of a DL signal. If a receivedsignal strength measured for each transmitting antenna in a userequipment among all transmitting antennas in DL is equal to or greaterthan a threshold, a corresponding antenna may be selected as atransmitting antenna. In this case, the transmitting antennas selectedby the user equipment in accordance with the antenna resource selectionreference may include the transmitting antennas located in a distanceadjacent to the corresponding user equipment as the antennas used by thebase station to support different user equipments. And, the transmittingantenna may include an antenna supportive of different DAS zones aswell.

The user equipment may be able to transmit the aforementioned feedbackinformation to the base station [S503].

Having received the feedback information, the base station finallydetermines a transmitting antenna in downlink per user equipment. Thedetermination of the antenna resource allocation may be made in the samemanner of the received feedback information or in consideration ofvarious conditions including feedback information, a load state of thebase station, intra-cell user equipment distribution, cooperation withan adjacent cell and the like [S504]. Thus, the base station makes thedetermination by considering other conditions together with the feedbackinformation. In particular, since the transmitting antennas selected bythe user equipment in accordance with the antenna resource selectionreference are the antennas used for the base station to support adifferent user equipment and are located in a distance adjacent to thecorresponding user equipment, they may include the antennas that maycause interference effect to communication between the correspondinguser equipment and the base station.

Subsequently, the base station may be able to transmit DAS controlinformation including the information on the transmitting antennafinally determined for the corresponding user equipment on a controlchannel, and preferably, on a dedicated control channel [S505].

In doing so, the DAS control information includes i) the number of thetransmitting antennas the base station intends to use for thecorresponding user equipment, ii) the index information of thetransmitting antenna the base station intends to use for thecorresponding user equipment, and iii) the information on a receivedsignal strength per transmitting antenna, which are described withreference to Table 1, and may further include iv) the number and/orindex information of the transmitting antennas determined to be used forthe corresponding user equipment by the base station among thetransmitting antennas fed back by the corresponding user equipment.

Likewise, since the transmitting antenna information on thecorresponding user equipment may be changed in accordance with alocation of the user equipment, a distance from each of the base stationantennas or the like, the DAS control information may be independentlyvariable per user equipment. Hence, the base station may be able totransmit the DAS control information by predetermined periods.Alternatively, the base station may be able to transmit the DAS controlinformation only if necessary for an event occurrence in the userequipment or the base station or the like.

Thereafter, the base station may be able to transmit a DL signal usingthe transmitting antenna finally determined for the corresponding userequipment [S506].

According to another embodiment of the present invention, a userequipment belonging to DAS transmits feedback information to a basestation in a manner that information on a pilot pattern is included aswell as information on a transmitting antenna.

FIG. 6 is a diagram for another example of a process for transceivingsignals between a base station and a user equipment in DAS according toone embodiment of the present invention.

Referring to FIG. 6, a user equipment enters a cell area in which a DASbase station provides a service and may then receive a DL signaltransmitted from the base station [S601].

Subsequently, the user equipment derives index information of a pilotpattern, which can be detected by the user equipment, via the receivedDL signal [S602].

In this case, the feedback information may further include vii) PPIinformation on transmitting antennas through DL signal measurement inthe user equipment as well as the feedback information described withreference to Table 3. The PPI determined by the user equipment may notbe equal to a PPI actually used by the base station in transmitting a DLsignal to the corresponding user equipment. And, a PPI determinedthrough a received signal in aspect of the user equipment may be named‘candidate PPI’.

Therefore, a candidate PPI determined by a user equipment may include aPPI supportive of communication with a different user equipment via anantenna located in an adjacent area of the corresponding user equipmentby causing interference as well as a PPI efficiently usable for acommunication between the corresponding user equipment and a basestation. Yet, information on an interference PPI may be optionallyincluded in feedback information. For instance, in a process describedin the following, if a base station determines a PPI to use for a userequipment, it may be able to derive an interference PPI by comparing thedetermined PPI to a PPI included in feedback information. Hence, theinterference PPI may not be included in the candidate PPI generated inthe step S602.

The user equipment transmits the generated feedback information to thebase station [S603]. The DAS control information may be independent andvariable per user equipment. Hence, the base station may be able totransmit the DAS control information by predetermined periods.Alternatively, the base station may be able to transmit the DAS controlinformation only if necessary for an event occurrence in the userequipment or the base station or the like.

Having received the feedback information, the base station may be ableto finally determine a transmitting antenna for the corresponding userequipment in consideration of various conditions including a load stateof the base station, intra-cell user equipment distribution, cooperationwith an adjacent cell and the like based on the feedback information[S604].

Thereafter, the base station may be able to transmit the DAS controlinformation including the information on the pilot pattern related tothe transmitting antenna finally determined for the corresponding userequipment on a dedicated control channel [S605].

Another example of DAS control information according to one embodimentof the present invention is described with reference to Table 4.

TABLE 4 DAS control information Description 1) Pilot Pattern i) PPIabout transmitting antennas determined to use, Indexes (PPI) ii) Indexset (excluded PPI) about PPI to be excluded from fed-back candidatePPIs, iii) Indicator of index sum (Index Agreement Indicator) 2) Radioresource Frequency/time division resource information of PPI informationon determined to use PPI 3) Pilot sequence Multiple orthogonal pilotsequence of PPI determined to use 4) Additional Information on an addedpilot pattern pilot pattern information

Referring to Table 4, DAS control information according to a furtherembodiment of the present invention includes 1) information on PPIsupported for communication with a corresponding user equipmentincluding at least one of: i) PPI information on transmitting antennasdetermined to use for the communication with the corresponding userequipment, ii) an index set (hereinafter named ‘excluded PPI (e-PPI)’)about PPI to be excluded from fed-back candidate PPI, and iii) Indicator(Index Agreement Indicator: IAI) of an index sum to indicate whether thesame PPI of the candidate PPI included in the feedback informationtransmitted from a user equipment is used.

In this case, if 1 bit is allocated for the index agreement indicator(e.g., if the index agreement indicator is set to 1), it may indicatethat the same PPI of the fed-back candidate PPI is used. If the indexagreement indicator is set to 0, it may indicate that a PPI unequal tothe fed-back candidate PPI is used.

If the base station determines to use the index unequal to the fed-backcandidate PPI in the step S604, the PPI information i) can be includedin the DAS control information. If the base station transmits theinformation on the PPI determined for the corresponding user equipmentin a manner that the information on the determined PPI is included inthe DAS control information, it may be efficient for a transmission ofthe antenna resource allocation information in case that the number ofactive user equipments is greater than the number of the base stationantennas distributed in the cell area.

Alternatively, the base station may have the e-PPI information ii)included in the DAS control information. Since the user equipmentgenerates the feedback information on the channel quality according tothe DL signal measurement and the transmitting antennas feasible for thecorresponding user equipment, the base station may be able to inform theuser equipment of the e-PPI information, which is preferably excluded insuing a pilot pattern, instead of transmitting the whole PPI informationdetermined to use for the corresponding user equipment. In doing so, theindex agreement indicator may be set to 0 or may not be included in theDAS control information.

In case of transmitting e-PPI, the base station may separately signale-PPI related information, which indicates whether the PPIs excludedfrom the feedback information are interference PPIs supportive of otheruser equipments or inactive, to the user equipment. Alternatively, thebase station may transmit the e-PPI related information to the userequipment in a manner that the corresponding information is included inthe DAS control information. For instance, while the base station isperforming communication with the corresponding user equipment inaccordance with a predetermined reference (e.g., if an interference rateof a specific antenna is equal to or greater than a predeterminedreference) in the fed-back candidate PPIs, if the base stationdetermines to turn off specific antennas, the base station may be ableto inform the user equipment that the e-PPIs excluded from the feedbackinformation are inactive.

In doing so, the e-PPI related information may be configured in a mannerthat indicators are enumerated in order preset for the PPIs excludedfrom the fed-back candidate PPIs. For instance, in case that the e-PPIrelated information is configured in a manner that 1-bit indicatorcorresponding to each pilot pattern is contiguously enumerated (e.g.,ascending order, descending order, etc.), if the 1-bit indicator is setto 0, it may indicate that the e-PPI is inactive. If the 1-bit indicatoris set to 1, it may indicate that the e-PPI is the interference PPI.

In case that the base station determines to use the PPI equal to thecandidate PPI included in the feedback information in the step S604 ofdetermining the transmitting antenna for the corresponding userequipment, the base station may be able to simplify a transmittedinformation size in a manner of transmitting the aforementioned indexagreement indicator set to 1.

Thus, the transmission of the e-PPI information as the information onthe transmitting antenna may be efficient for a case that the totalnumber of antennas of the base station is greater than that of theactive user equipments located within a cell area. This is useful for acase that the base station transmits the index agreement indicator onlywithout transmitting separate information on PPI in a manner of usingthe PPI equal to the fed-back candidate PPI.

Referring to table 4, a base station may be able to transmit DAS controlinformation in a manner that frequency/time division information of apilot pattern used for a user equipment is further included in the DAScontrol information.

Regarding the frequency/time division information of the pilot pattern,this information is the information notified to a user equipment in casethat a base station differently allocates frequency/time resources forantenna resource allocation per user equipment. In DAS, radio resourcesmay be allocated in a manner of being multiplexed per antenna or antennagroup. For instance, it may be able to use FDM scheme of dividingfrequency band to use or TDM scheme of dividing time band to use.

For example, when a radio resource is allocated per antenna by FDM, ifthe distributed antennas 1, 2, 7 and 8 are allocated to the UE 1 shownin FIG. 1, all the antennas 1, 2, 7 and 8 may be configured to be usedon a 1^(st) frequency band and the antennas 1, 2 and 7 may be configuredto be used on a 2^(nd) frequency band only. Hence, a base station may beable to transmit resource information on frequency or time band, whichis used for each of a plurality of specific antennas allocated to aspecific user equipment, to a corresponding user equipment.

Referring to Table 4, a base station may be able to transmit DAS controlinformation in a manner that pilot sequence information (e.g., multipleorthogonal pilot sequence information) in a pilot pattern used per userequipment or pilot pattern information added for pilot pattern additionis further included in the DAS control information.

In order to facilitate channel estimation, the user equipment mayconsider at least one of the frequency/time division information ofpilot pattern used per user equipment, the pilot sequence information inthe pilot pattern and the additional pilot pattern in theabove-mentioned DAS control information.

The base station may be able to transmit the DAS control information bypredetermined periods. Alternatively, the base station may be able totransmit the DAS control information only if necessary for an eventoccurrence in the user equipment or the base station or the like.

Thereafter, the base station may be able to transmit a signal using aspecific transmitting antenna for a communication with the correspondinguser equipment via the DAS control information [S607].

Meanwhile, according to a further embodiment of the present invention, auser equipment may be able to transmit PPI information preferred to beused for a communication with a base station. This is described withreference to Table 5 as follows.

Table 5 shows another example of feedback information generated by auser equipment belonging to DAS according to one embodiment of thepresent invention.

TABLE 5 Feedback information i Received signal strength for eachtransmitting antenna used in DL ii Received signal strength of at leastone transmitting antenna selected by a user equipment from alltransmitting antennas used in DL iii Number of transmitting antennasrequested again by a user equipment iv Number of transmitting antennasmeeting an antenna resource selection reference v Index information of atransmitting antenna requested again by a user equipment among alltransmitting antennas in DL vi Index information of a transmittingantenna meeting an antenna resource selection reference among alltransmitting antennas in DL vii Preferred pilot pattern indexes (PPPI)information 1 Channel state information estimated from each PPIbelonging to PPPI 2 Preferred order of pilot pattern indexes belongingto PPPI 3 Specific number of maximum preferred patterns and theirchannel state information among pilot pattern indexes belonging to PPPI

Referring to Table 5, another example of feedback information accordingto one embodiment of the present invention may further include vii)preferred pilot pattern indexes (PPPI) information on transmittingantennas determined by a user equipment as well as the former feedbackinformation described with reference to Table 3.

In this case, ‘PPPI’ may be defined as a pilot pattern index indicatingthat a received signal strength of a channel estimated via a commonpilot, a channel gain or the like exceeds a predetermined threshold inaspect of a user equipment. The information on the PPPI may betransmitted by predetermined periods in accordance with a speed of auser equipment, a DAS antenna configuration or the like without beingincluded in DAS control information. Alternatively, the information onthe PPPI may be transmitted as a separate signal if necessary for a caseof an event occurrence in a base station or a user equipment.

Moreover, as feedback information that can be provided together with thePPPI to raise performance of a base station in resource management suchas scheduling between user equipments in a base station, resourceallocation and the like, a user equipment may be able to transmit atleast one of {circle around (1)} channel state information estimatedfrom each PPI belonging to PPPI, {circle around (2)} preferred order ofpilot pattern indexes belonging to PPPI, and {circle around (3)}specific number (M) of maximum preferred patterns and their CSI (channelstate information) among pilot pattern indexes belonging to PPPI.

The CSI is a general information related to a channel state and includesa channel coefficient, a channel gain, a covariance matrix related tothe channel gain, modulation and coding level information and the like.

The {circle around (1)} CSI (channel state information) estimated fromeach PPI belonging to PPPI is to feed back a state information of achannel estimated from each pilot pattern and may be transmittedsimultaneously with or separately from preferred orders of pilot patternindexes belonging to PPPI.

Information on the {circle around (2)} preferred order of pilot patternindexes belonging to PPPI is not separately signaled but may be notifiedin a manner of transmitting the ordered PPPI enumerated in preferredorder in case of PPPI transmission.

The {circle around (3)} specific number of maximum preferred patternsand their channels state information among pilot pattern indexesbelonging to PPPI is to feed back a specific number of maximum preferredpilot patterns and channel states respectively corresponding to thepilot patterns to reduce overhead of the information {circle around (1)}and {circle around (2)}.

If the information on the specific number (M) of the maximum preferredpilot patterns is set in a manner of being included in a configurationparameter of a system, all user equipments entering a corresponding cellmay be able to transmit the same number of maximum preferred pilotpattern index information. In case that a base station makes adetermination of the corresponding information by a cell unit, a userequipment configures feedback information in accordance with a maximumpreferred number (M) in PPPI transmitted by a base station. Hence, sincethe corresponding information may vary in accordance with indicationinformation transmitted by the base station, it may be independent foreach user equipment. In case that a user equipment arbitrarily makes thedetermination, the corresponding information may depend on such areference as the number of CSIs having a link quality exceed a specificthreshold, a required data size, a preference and the like.

If it is instructed to feed back a specific number of PPPIs inaccordance with an indication made by a base station among PPPIsdetermined by a user equipment or a preset specific number of maximumpreferred pilot pattern index information in an initial configuration ofa corresponding system is transmitted with ordered PPPI, CSI(hereinafter named best-M CSI) on a predetermined number (M) of channelsin most upper state can be transmitted together. In particular, thefeedback information including PPPI according to one embodiment of thepresent invention may include at least one of the ordered PPPItransmitted in the preferred order, CSI corresponding to the orderedPPPI and all PPPI, and the ordered PPPI and best-M CSI.

The base station receiving the feedback information exemplarily shown inTable 5 may be able to transmit the DAS control information describedwith reference to Table 4 to the user equipment. Yet, in this case, theDAS control information may be able to include at least one of i) PPIinformation on transmitting antennas determined to use for thecommunication with the corresponding user equipment, ii) an index set(hereinafter named ‘excluded PPI (e-PPI)’) about PPI to be excluded fromfed-back candidate PPI, and iii) Indicator (Index Agreement Indicator:IAI) of an index sum to indicate whether the same PPI of the candidatePPI included in the feedback information transmitted from a userequipment is used.

Theses feedback information are the information usable when a basestation belonging to DAS determines to allocate a transmitting antennaper user equipment. Theses feedback information may be transmitted byfeedback by predetermined periods in accordance with a speed of a userequipment, a DAS antenna configuration or the like. Alternatively, thesefeedback information may be transmitted in case of an event occurrencein a user equipment.

In case that DAS is used in 3GPP LTE, feedback information according toembodiments of the present invention may be transmitted to a basestation via a physical uplink control channel (PUCCH) or a physicaluplink control channel (PUSCH). In case that DAS is used in IEEE 802.16,feedback information according an embodiment of the present inventionmay be transmitted to a base station via an uplink primary fast feedbackchannel (PFBCH) or an uplink secondary fast feedback channel (SFBCH).Alternatively, the feedback information may be transmitted on a channelnewly defined for DAS.

3. 3^(rd) Embodiment Deriving Logical Antenna Index from Pilot PatternIndex

In a conventional CAS based communication system, since all physicalantennas of a base station join in transmission and reception withusers, it may be unnecessary to discriminate a logical antenna index(LAI) or PPI from physical antenna indexes (PAI).

Yet, in a DAS based communication system, since a plurality of antennasmay use the same pilot pattern, each user equipment may operate byrecognizing DAS antenna not on the basis of PAI but on the basis of PPI.In particular, in aspect of a user equipment, PAI and PPI may bediscriminated from each other.

In DAS, each antenna is allocated to a specific one of antenna sets eachof which consists of a partial set of all available PPI or PAI. Forinstance, referring to FIG. 1, assuming that all antennas of DAS systemare 8 Tx and that the system is set to have PPI=PAI=8, when a basestation transmits data on 4 Tx by allocating PPI of antennas #1, #2, #7and #8 to UE 1, if the user equipment attempts to feed back PMI, it mayhave to select a most upper matrix from a precoding matrix codebookcorresponding to 4 Tx.

In doing so, column vectors (or row vectors) of each codebook should bemapped to the antennas #1, #2, #7 and #8, respectively. And, indexes forproviding this process consistently and serially are required.

Moreover, according to the above-described embodiments of the presentinvention, in case that PPI used per user equipment is determined andinformation on the PPI is transmitted, each user equipment deriveschannel related information such as CQI, PMI, covariance matrix and thelike using the received PPI and may be then able to transmit the derivedchannel related information to a base station by feedback. Since PPIsallocated per user equipment are an arbitrary partial set of anavailable PPI set, consistent and serial antenna indexes are required inorder for each user equipment to use and measure information related toa channel using the PPIs.

Therefore, according to another embodiment of the present invention, aDAS base station may be able to use LAI as index information on a basestation antenna used for a communication with each user equipment. Inthis case, assuming that the number of maximum base station antennascorresponding to a specific user equipment is set to N_Tx(k), the LAImay be configured with integers ranging 0 to maximum ‘N_Tx(k)−1’ orranging 1 to N_Tx(k).

A base station antenna corresponding to each user equipment may includeone of a transmitting antenna used for a base station to transmit a DLsignal to a specific user equipment, a base station antenna interferingwith a specific user equipment and an interfering antenna interferingwith a specific user equipment. For instance, the UE 1 shown in FIG. 1may be able to receive a signal from at least one of the antennas 1, 2,7 and 8. And, the antenna 7 may correspond to an interfering antennalocated within a coverage supportive of the UE 1 and may have aninterference influence on the UE 1 while supporting the UE 2. Hence, theantennas corresponding to the UE 1 include all antennas actually used bya base station to transmit data to the UE 1 and the correspondinginterfering antennas, and more particularly, the antennas 1, 2, 7 and 8.

Thus, in aspect of a user equipment, since the number of base stationantennas for transmitting data may not be equal to the number ofinterfering antennas, LAIs may be discriminated into two different typessuch as dedicated LAI and interfering LAI for example.

FIG. 7 is a diagram for one example of a process for a DAS base stationto transmit signals to a user equipment according to one embodiment ofthe present invention. This process may be performed in the same mannerof the former embodiment described with reference to FIG. 4.

Referring to FIG. 7, since a step S701 for a base station to receive aUL signal from a user equipment, a step S702 for the base station todetermine PPI for the corresponding user equipment among all antennas ofthe base station based on a result of measuring strength of the receivedUL signal, and a step S703 of transmitting DAS control informationincluding PPI as information on a transmitting antenna may correspond tothe former steps S401 to S403 shown in FIG. 4, their details shall beskipped for clarity of the following description.

In this case, the DAS control information includes the former PPIdescribed with reference to Table 2, which is to be used for each userequipment, and may optionally include information on the interfering PPIhaving an interference influence on the corresponding user equipment.

Having received the DAS control information, the user equipment performsa process for mapping the received PPI to LAI [S704]. The process formapping the PPI or PAI to the LAI may be performed in a manner ofconfiguring the LAI in ascending or descending order or mapping the PAIin accordance with such a specific performance reference as a power gainper PPI and the like. Mapping PPI or PAI to LAI may be performed in thesame manner of uplink or downlink or by an independent scheme.

Meanwhile, since the base station should be aware of this correspondingrelation between PPI or PAI and LAI, the user equipment may be able totransmit information on an LAI mapping rule to the base station [S705].

Subsequently, the user equipment selects PMI from a precoding matrixcodebook based on the configured LAI, generates feedback information bymeasuring channel related information such as CQI, covariance matrix andthe like, and may be then able to transmit the generated feedbackinformation to the base station [S706]. In particular, the feedbackinformation is transmitted simultaneously together with the LAP mappinginformation or may be transmitted by separate signaling.

Thereafter, the base station may be able to transmit a DL signal to theuser equipment via the determined PPI [S707].

In particular, in UL signal transmission, the user equipment converts achannel corresponding to base station receiving antenna PPI or PAI toLAI and may be able to use it for channel estimation and relatedprecoding. The base station converts a signal received via antennascorresponding to the reception PPI or PAI of the corresponding userequipment to LAI having serial property and may then perform decoding.

The signal transceiving process between the DAS base station and theuser equipment according to one embodiment of the present inventiondescribed with reference to FIG. 7 shows one example for a base stationto determine an antenna specified to a user equipment by measuring a ULsignal.

On the other hand, a user equipment selects at least one or moreantennas corresponding to the user equipment from all antennas of a basestation based on a result of measuring a DL signal and may be then ableto perform mapping PPI or PAI to LAI on the corresponding antennas.

FIG. 8 is a diagram for another example of a process for a DAS basestation to transmit signals to a user equipment according to oneembodiment of the present invention. This process may be performed inthe same manner of the former embodiment described with reference toFIG. 6.

Referring to FIG. 8, a user equipment receives a DL signal transmittedfrom a base station [S801].

The user equipment generates information on a transmitting antenna in amanner of measuring the received signal and then selecting antennas eachof which meets received signal strength or the like [S802] and may bethen able to transmit the generated information to the base station[S803].

For instance, a physical antenna set of DAS system having 32 basestation antennas is ‘PMI set={1, 2, . . . 32}. In this case, if 4 PAIsspaced far apart from each other are mapped by one PPI using 8 PPIs(i.e., PPI set={1, 2, . . . 8}, antennas 1, 9, 17 and 25 can be regardedas using the same pilot pattern. Hence, ‘PAI set={1, 9, 17, 25}’ may bemapped to ‘PPI=1’. The user equipment determines ‘PPI set={1, 2, 4}’configured with PPIs, each of which meets a received signal strengthover a predetermined reference, among 8 PPIs at its location and may bethen able to transmit feedback information on the determination to thebase station.

Having received a UL signal including the feedback information, the basestation may be then able to determine an antenna, which can be specifiedto a communication with the corresponding user equipment, via thefeedback information, the UL reception strength and the like [S804].

According to the above embodiment, the base station may be able todetermine to use the antennas 9, 10 and 12 (i.e., PAI set={9, 10, 12})for the corresponding user equipment based on the received signalstrength among the transmitting antennas corresponding to ‘PPI set={1,2, 4} in the feedback information transmitted from the correspondinguser equipment.

Subsequently, the base station transmits DAS control informationincluding the information on the transmitting antenna finally determinedfor the corresponding user equipment to the user equipment [S805]. Thebase station may inform the corresponding user equipment that DL datawill be transmitted via 3 Tx of the antennas 9, 10 and 12 (i.e., PAIset={9, 10, 12}) to the corresponding user equipment.

Having received the information on the finally determined transmittingantenna via the DAS control information, the user equipment performs aprocess for mapping the received PPI to LAI [S806]. According to theabove embodiment, if the user equipment sets a power gain per PPI withreference to performance, the mapping may be performed in a manner ofestablishing one-to-one correspondence between ‘LAI={1, 2, 3}’ and‘PPI={2, 1, 4}’ in order of each per-PPI power gain in ‘PPI={1, 2, 4}’.

Subsequently, the user equipment may be able to transmit by feedback theLAI mapping information, which indicates the mapping to LAI withreference to a power gain size of each PPI, to be base station [S807].In doing so, since the user equipment fed back the preferred pilotpattern index (PPPI) in the preferred order in the step S802, if the PPIis mapped to the LAI in the preferred PPI order, the base station may beable to derive the mapping information indicating that the userequipment has mapped the PI to the LAI. Hence, it may be unnecessary totransmit the separate mapping information in the step S806.

Subsequently, the user equipment derives channel related informationbased on the established LAI and may be then able to transmit thederived channel related information to the base station by feedback[S808]. For instance, when the number of antenna of a user equipment is1, channel coefficients h₁, h₂ and h₃ corresponding to LAI 1, LAI 2 andLAI 3 are estimated using channels estimated from ‘PPI set={1, 2, 4}’and all vector channels ‘h=[h₁, h₂, h₃]’ can be then derived through theestimated channel coefficients. When a 3 tx precoding matrix codebookconsists of 3 rows×r columns matrixes (where r is the number of datastreams, i.e., 3), it may be able to find PMI and CQI through sizecomparison and the like by performing inner product on each of thematrixes of the codebook by h. Alternatively, when such information on achannel as a channel coefficient, a covariance matrix and the like istransmitted to a base station, it may be able to use a channel sorted byLAI.

Since the number of physical antennas corresponding to each userequipment belonging to DAS is not identical, a range of LAI may not beidentical for each user equipment. Hence, a physical antenna index(PAI), a pilot pattern index (PPI) and a logical antenna index (LAI) maynot be identical for one user equipment.

Thereafter, the base station may be able to transmit a DL signal to theuser equipment using the transmitting antenna determined to use for thecorresponding user equipment [S809].

In uplink, a user equipment converts a channel corresponding to PPI (orPAI) for a UL receiving antenna to LAI, performs channel estimationusing the LAI, and may then transmit a precoded signal to a basestation. Having received the precoded signal, the base station convertssignals received from antennas corresponding to the reception PPI (orPAI) of the corresponding user equipment to LAI having serial propertyand may then perform decoding.

Meanwhile, in case that an LAI mapping method according to oneembodiment of the present invention is applied to LTE/LTE-A system, anantenna port index (API) may be mapped to LAI. To this end, PAI ismapped to API and the API may be then mapped to LAI.

DAS control information according to embodiments of the presentinvention may be able to configure antenna resource allocation, which isused for one user equipment, to differ per frequency band by applying acase of using FDM for radio resource allocation. In case that antennaresource allocation differing per frequency band is applied, feedbackinformation and/or DAS control information according to embodiments ofthe present invention may be transmitted per frequency band.

In doing so, by transmitting an indicator indicating whether feedbackinformation and/or DAS control information of the rest of thefrequencies except the specific frequency band is different from that ofthe specific frequency band, a transmitted information size may bereduced or a transmission accuracy may be raised. In particular,feedback information and/or DAS control information may be transmittedon a specific frequency band for a corresponding user equipment and anindicator indicating whether the feedback information and/or DAS controlinformation transmitted on the specific frequency band is independentfrom that transmitted on the rest of the frequency band except thespecific frequency band may be transmitted.

Therefore, if feedback information and/or DAS control informationtransmitted on a specific frequency band is identical to feedbackinformation and/or DAS control information transmitted on a frequencyband other than the specific frequency band, an indicator indicating theidentity is transmitted only. Otherwise, feedback information and/or DAScontrol information corresponding to the corresponding frequency bandmay be transmitted only.

Alternatively, only if information transmitted on a discriminatedfrequency band is not identical without transmitting a separateindicator, feedback information and/or DAS control information, which isto be transmitted, may be transmitted on a corresponding frequency band.

The above-described embodiments of the present invention may beperformed on an independent network configured with DAS cells only in asystem supportive of DAS or may be used together with a conventional CASsupportive system.

In case of a system using CAS and DAS together, a base station may beable to transmit information indicating that DAS is supported for userequipments entering a cell in the corresponding system.

When user equipments initially enter a DAS supportive cell, a basestation according to one embodiment of the present invention may be ableto broadcast a broadcast information including cell ID information, DASsupport indication information indicating whether a corresponding systemsupports DAS, and the like into a cell area. In this case, the broadcastinformation may include the cell ID information, the DAS supportindication information, information on a pilot pattern used in acorresponding cell, information on the number of maximum pilot patternsto support and the like.

In doing so, the base station may be able to directly notify the userequipments, which initially enter the cell, whether the base stationsupports CAS or DAS through the DAS support indication information.

Alternatively, DAS support indication information may be configured tobe included in cell ID information. In case that the DAS supportindication information is indicated via the cell ID information, cell IDis configured to include information for discriminating CAS and DAS fromeach other. Hence, a user equipment having received the cell ID may beable to derive whether the base station currently supports CAS or DASthrough the cell ID.

For instance, a cell ID in IEEE 802.16 system is hierarchicallyclassified in accordance with a base station type such as a macrocellbase station (BS), a hot zone base station (BS), a femto cell basestation (BS) and the like. When the cell ID is configured in accordancewith a type of a corresponding base station, an upper or lower layer maybe discriminated to indicate whether the corresponding base stationsupports CAS or DAS. In IEEE 802.16 system, cell ID is broadcasted viaPA-preamble and SA-preamble.

For another instance, in LTE-A, a base station transmits cell ID into acell area via CRS. In doing so, a portion of a signal configuring thecell ID may be assigned as a signal indicating a DAS supportive system.Alternatively, it may be able to configure a separate cell ID byclassifying a system into CAS or DAS.

Base station and user equipment belonging to DAS for implementingembodiments of the present invention are described with reference toFIG. 9 as follows.

FIG. 9 is a block diagram of a base station and a user equipment toimplement embodiments of the present invention.

First of all, a user equipment works as a transmitter in uplink and isable to work as a receiver in downlink. A base station works as areceiver in uplink and is able to work as a transmitter in downlink. Inparticular, each of the user equipment and the base station includes atransmitter and a receiver for transmission of information and/or data.

Each of the transmitter and the receiver can include a processor, amodule, a part and/pr a means for performing embodiments of the presentinvention. In particular, each of the transmitter and the receiver caninclude a module (means) for encrypting a message, a module forinterpreting the encrypted message, an antenna for transceiving themessage and the like.

Referring to FIG. 9, a left part in the drawing represents a basestation belonging to DAS with a structure of a transmitter, while aright part in the drawing represents a user equipment entering a cell,which enters a cell serviced by the DAS base, with a structure of areceiver. The transmitter/receiver may include an antenna 901/902, areceiving module 910/920, a processor 930/940, a transmitting module950/960 and a memory 970/980.

The antenna 901/902 includes a receiving antenna performing a functionof receiving a radio signal externally and then delivering the receivedradio signal to the receiving module 910/920 and a transmitting antennaexternally transmitting a signal generated from the transmitting module950/960. In case that a multiple-antenna (MIMO) function is supported,at least two antennas can be provided to the user equipment or the basestation.

The antenna 901 of the transmitter shown in FIG. 9 indicates at leastone DA selected from all antennas of the base station based on a channelstate, a location of the user equipment, a distance between the basestation and the user equipment and the like in the course ofcommunication. The selected at least one DA is not fixed but may bechangeable in accordance with a location change of the receiver or thelike.

The receiving module 910/920 reconstructs the radio signal receivedexternally via the antenna into original data in a manner of performingdecoding and demodulation on the received radio signal and may be thenable to deliver the reconstructed original data to the processor930/940. The receiving module and the antenna may not be separated fromeach other as shown in FIG. 9. Instead, the receiving module and theantenna may be represented as a receiving unit configured to receive aradio signal.

The processor 930/940 generally controls overall operations of thetransmitter or the receiver. In particular, the processor 930/940 may beable to perform a controller function for performing the above-describedembodiments of the present invention, a MAC (medium access control)frame variable control function according to service characteristics andpropagation environment, a handover function, an authenticationfunction, an encryption function and the like.

The transmitting module 950/960 performs predetermined coding andmodulation on a signal and/or data, which is scheduled by the processor930/940 and will be then transmitted externally, and may be then able todeliver the coded and modulated signal and/or data to the antenna. Thetransmitting module and the antenna may not be separated from each otheras shown in FIG. 9. Instead, the transmitting module and the antenna maybe represented as a transmitting unit configured to transmit a radiosignal.

The memory 970/980 may store programs for processing and control of theprocessor 930/940 and may be able to perform a function of temporarilystoring input/output data (e.g., in case of the user equipment, UL grantallocated by the base station, system information, station identifier(STID), a flow identifier (FID), an action time, etc.).

And, the memory 970/980 may include at least one of storage mediaincluding a flash memory, a hard disk, a multimedia card micro typememory, a memory card type memory (e.g., SD memory, XD memory, etc.), aRAM (random access memory), an SRAM (static random access memory), a ROM(read-only memory), an EEPROM (electrically erasable programmableread-only memory), a PROM (programmable read-only memory), a magneticmemory, a magnetic disk, an optical disk and the like.

The processor 930 of the transmitting stage performs overall controloperations on the base station. The processor 930 may perform antennaresource allocation for selecting a transmitting antenna or an antennagroup for each user equipment according to the embodiments of thepresent invention described with reference to FIGS. 3 to 8 or may beable to configure a pilot pattern index (PPI) corresponding to each userequipment.

The processor 930 of the transmitting stage may be able to configure DAScontrol information including configuration information on DAS system,information on a antenna or an antenna group to be used for acommunication with each user equipment or information on PPI.

The receiver receives the signal and DAS control information transmittedfrom the transmitter via the receiving module 920 and may be then ableto acquire various configuration information on the DAS system and theinformation on the antenna or the antenna group used for thecommunication with the transmitter.

The processor 940 of the receiver performs overall control operations onthe user equipment. The processor 940 may be able to generate feedbackinformation on a channel state by measuring a DL signal transmitted fromthe transmitter. Moreover, the processor 940 determines a base stationantenna corresponding to the receiver through a received signal strengthof the DL signal by the embodiments described with reference to FIG. 5and FIG. 6 and may be then able to inform the transmitter of theinformation on the determination. Moreover, the processor 940 convertsPPI or PAI transmitted from the transmitter by the embodiments describedwith reference to FIG. 7 and FIG. 8 to LAI, generates feedbackinformation based on the LAI, and may be then able to transmit thegenerated feedback information to the transmitter.

Meanwhile, the base station may perform a controller function forperforming the above-described embodiments of the present invention, anOFDMA (orthogonal frequency division multiple access) packet scheduling,TDD (time division duplex) packet scheduling and channel multiplexingfunction, a MAC (medium access control) frame variable control functionaccording to a service characteristic and electric wave environment, afast traffic real-time control function, a handover function, anauthentication and encryption function, a packet modulation/demodulationfunction for data transmission, a fast packet channel coding function, areal-time modem control function, and the like using at least one of themodules mentioned in the foregoing description and may further includemeans, modules, parts and/or the like to perform these functions.

As mentioned in the foregoing description, the detailed descriptions forthe preferred embodiments of the present invention are provided to beimplemented by those skilled in the art. While the present invention hasbeen described and illustrated herein with reference to the preferredembodiments thereof, it will be apparent to those skilled in the artthat various modifications and variations can be made therein withoutdeparting from the spirit and scope of the invention. Thus, it isintended that the present invention covers the modifications andvariations of this invention that come within the scope of the appendedclaims and their equivalents. For instance, the respectiveconfigurations disclosed in the aforesaid embodiments of the presentinvention can be used by those skilled in the art in a manner of beingcombined with one another.

Therefore, the present invention is non-limited by the embodimentsdisclosed herein but intends to give a broadest scope matching theprinciples and new features disclosed herein.

INDUSTRIAL APPLICABILITY

Accordingly, embodiments of the present invention are applicable to abase station, a user equipment and other devices in a wirelesscommunication system.

1. A method of receiving a signal, which is received from a base stationby a user equipment in a distributed antenna system (DAS), the methodcomprising the steps of: 1) receiving control information on at leastone effective transmitting antenna allocated to the user equipment amonga plurality of antennas from the base station including the plurality ofantennas; and 2) receiving the signal via the at least one effectivetransmitting antenna from the base station.
 2. The method of claim 1,wherein the control information comprises at least one selected from thegroup consisting of information on the number of the at least oneeffective transmitting antenna, index information of the at least oneeffective transmitting antenna and received signal strength informationfor each of the plurality of antennas.
 3. The method of claim 2, furthercomprising the step of mapping at least one PAI to logical antennaindexes (LAI) according to a predetermined mapping rule.
 4. The methodof claim 3, wherein the predetermined mapping rule configures the LAIwith an index of the effective transmitting antenna in performance orderaccording to a power gain for each effective transmitting antenna. 5.The method of claim 1, wherein the control information comprises atleast one selected from the group consisting of information on one ormore pilot pattern indexes (PPI) supportive of the user equipment andinformation on PPI having an interference influence on the userequipment.
 6. The method of claim 1, further comprising the step oftransmitting feedback information including antenna related informationused for a transmission of a downlink signal based on the downlinksignal received from the base station by the user equipment to the basestation before the step 1), wherein the control information isdetermined by the base station based on the feedback information.
 7. Themethod of claim 6, wherein the feedback information comprises at leastone selected from the group consisting of a received signal strength foreach of the plurality of antennas, a received signal strength for atleast one antenna selected from the plurality of antennas by the userequipment, information on the number and/or indexes of antennas meetinga predetermined selection reference, and candidate PPI meeting apredetermined selection reference.
 8. The method of claim 7, wherein theinformation on the indexes of antennas fed back by the user equipment istransmitted via a bitmap.
 9. The method of claim 7, wherein thepredetermined selection reference comprises whether a received signalstrength of the downlink signal received via a portion of the pluralityof antennas is equal to or greater than a reference value.
 10. Themethod of claim 9, wherein information on the reference value isreceived from the base station.
 11. The method of claim 6, wherein thefeedback information comprises preferred pilot pattern indexes (PPPI)requested by the user equipment and wherein the PPPI comprises at leastone PPI in which a received signal strength or a channel gain of achannel estimated via a common pilot transmitted from the base stationmeets a value equal to or greater than a predetermined reference value.12. The method of claim 11, wherein the PPPI is transmitted via a bitmap.
 13. The method of claim 11, wherein the feedback informationfurther comprises at least one selected from the group consisting ofchannel state information estimated from each PPI included in the PPPI,a preferred order of at least one PPI included in the PPPI, a specificnumber of most preferred PPIs among the at least one PPI included in thePPPI, and channel state information on the specific number of the mostpreferred PPIs.
 14. The method of claim 13, wherein the specific numberof the most preferred PPI corresponds to one selected from the groupconsisting of system configuration parameter information, indicationinformation determined and transmitted by the base station, andinformation arbitrarily determined by the user equipment.
 15. The methodof claim 7, wherein the control information comprises at least oneselected from the group consisting of information on specific pilotpattern indexes (PPI) supportive of the user equipment, an index set(excluded PPI: e-PPI) supposed to be excluded from the candidate PPI orthe PPPI fed back from the user equipment, and an index agreementindicator indicating whether PPI equal to the candidate PPI or the PPPIfed back from the user equipment is used.
 16. The method of claim 15,wherein if the index agreement indicator is set to indicate theinformation indicating that the PPI equal to the candidate PPI or thePPPI fed back from the user equipment is used, the control informationdoes not comprise information on the specific PPI and the e-PPI.
 17. Themethod of claim 15, further comprising the step of mapping the specificPPI to LAI by a predetermined mapping rule.
 18. The method of claim 17,wherein the predetermined mapping rule comprises configuring the LAI inperformance order according to power gain for each of the PPI.
 19. Themethod of claim 4, further comprising the steps of: estimating channelrelated information based on the LAI; and transmitting the channelrelated information to the base station by feedback.
 20. The method ofclaim 4, further comprising the step of transmitting information on thepredetermined mapping rule to the base station.
 21. The method of claim1, wherein the control information is independently configured for eachuser equipment belonging to the DAS and wherein the control informationis determined independently in accordance with at least one of alocation of the user equipment and a frequency band used by the userequipment.
 22. The method of claim 1, further comprising the step ofreceiving indication information indicating that the system supports atleast one of the DAS and a centralized antenna system from the basestation when the user equipment enters a cell area in which the basestation provides a service.
 23. The method of claim 22, wherein theindication information is transmitted via cell ID.
 24. A user equipmentin a distributed antenna system (DAS), comprising: a receiving moduleconfigured to receive a signal; a processor configured to generate afeedback information on a distributed antenna of a base station used fora downlink transmission based on a downlink signal received from thebase station including a plurality of antennas spaced apart from apredetermined distance via the receiving module; and a transmittingmodule configured to transmit the feedback information to the basestation, wherein the processor is configured to receive controlinformation on at least one effective transmitting antenna to be usedfor a communication with the user equipment among the plurality ofantennas from the base station via the receiving module.